1. Field of Invention
The present invention relates to an oil cooler and an EGR (Exhaust Gas Recirculation) cooler for a vehicle, and particularly to an integrated cooler system for a vehicle which makes it possible to greatly reduce the time needed to reach the warm up of oil by facilitating the oil to have a heat exchange with the EGR gas at the time of a cold start, while ensuring that a driving force loss of a water pump can be reduced in such a way to minimize the differential pressure of cooling water of an EGR cooler circuit.
2. Description of Related Art
The EGR gas, which generally uses an exhaust gas, should be carefully handled to minimize generation of NOx due to a high temperature, whereas the engine oil, which is generally used to lubricate an oil pump and a friction portion between a cylinder block and a piston and a crank shaft and other engine elements, should be carefully managed so the engine oil will not be at a low temperature having a high kinematic viscosity. Here, EGR represents Exhaust Gas Recirculation.
For this, the EGR gas circulates along an EGR cooler configured to perform a heat exchange operation with cooling water (or anti-freezing solution), thus preventing a high temperature state which might causes NOx to generate.
In addition, since the engine oil circulates along an oil cooler configured to perform a heat exchange operation with cooling water, thus preventing a low temperature state which might lower friction force. In particular, because the engine oil is heated by cooling water, the oil temperature can quickly warm up in a cold state when a vehicle drives, so the friction force can be reduced at the lubricating parts of an engine, thus enhancing the fuel efficiency of a vehicle.
The source of heat to increase the temperature of cooling water is a combustion (including EGR gas) energy generated at the engine, and the engine heat generated from combustion is needed to be more efficiently used. Examples of utilizing the engine heat include a heat storage (HE) technology directed to storing residual heat and supplying heat at the time of cold operation, and an exhaust heat recirculation system (EHRS) directed to enhancing a warm up characteristic by re-circulating exhaust gas waste heat which used to be wasted. Both the HE (Heat Storage) technology and the EHRS (Exhaust Heat Recirculation System) technology are directed to quickly increasing the temperature of cooling water or oil, thereby enhancing the combustion efficiency and improving fuel efficiency.
When a cooler system is formed of an EGR cooler, an oil cooler and cooling water, the EGR gas line is configured to directly pass through the EGR cooler or is configured to have a layout with a bypass; however the cooling water line is configured to have a layout passing through the EGR cooler all the time.
The above mentioned constructions are provided since the engine oil has to absorb heat from high temperature cooling water (anti-freezing solution) so that it does not have a high kinematic viscosity, whereas the EGR gas has to emit heat to low temperature cooling water (anti-freezing solution) so that the temperature can be lowered.
The above mentioned cooler system needs inevitably an indirect heat exchange operation between an EGR cooler and an oil cooler with cooling water being used as a medium. Such a system takes long time to increase the oil temperature during a cold operation, causing a discharge pressure of an oil pump to increase.
As an example, the increase of the discharge pressure of the oil pump results in an increase of the oil pressure, and the increase of the oil pressures results in an increase of a jointing pressure in the engine friction system, so the friction force of the engine driving system is lowered. In particular, the low temperature oil has a high kinematic viscosity and a high oil pressure, thereby lowering the wear resistances of the engine elements and generating noises. As a result, the durability of the engine might be greatly lowered.
So, the layout for a cooling water circulation in the EGR cooler and the oil cooler is important for the temperature control of gas such as EGR gas and fluid such as engine oil by way of a heat exchange (heating and cooling).
Since the cooling water line has a layout passing through the EGR cooler all the time, any disadvantages occurring in an independent cooler system formed of an oil cooler and an EGR cooler cannot be overcome. Also, since it takes long time to increase oil temperature during a cold operation, the discharge pressure of an oil pump increases, and the oil pressure increases due to the increase of the discharge pressure of the oil pump. As such, the jointing pressure in the engine friction system increases, and the friction force in the engine driving system increases. Further, the low temperature oil has a high kinematic viscosity and a high oil pressure, thereby lowering the wear resistances of the engine elements and generating noises. As a result, the durability of the engine might be greatly worsened.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.